A study finds that users of reusable contact lenses are four times more likely than those who wear everyday disposables to develop a rare sight-threatening eye infection.
Researchers suggest that people avoid wearing their lenses while swimming or while showering, and the package should contain “no water” stickers.
The study identified several factors that increase the risk of developing AK, including reusing the lenses, wearing them overnight or while showering.
AK is a type of corneal infection, a condition that leads to inflammation of the cornea – the eye’s clear, protective outer layer.
Researchers estimate that 30-62% of cases of the condition in the UK, and possibly in many other countries, could be prevented if people switched from reusable lenses to daily disposable lenses.
Lead author Professor John Dart, from the UCL Institute of Ophthalmology and Moorfields Eye Hospital NHS Foundation Trust, said: ‘In recent years we have seen an increase in Acanthamoeba keratitis in the UK and Europe, and although the infection is still rare, it is preventable and warrants public health response.
Contact lenses are generally very safe but are associated with a small risk of bacterial keratitis, which is mostly caused by bacteria, and is the only sight-threatening complication from their use.
“Given that an estimated 300 million people worldwide wear contact lenses, it is important for people to know how to reduce their risk of developing keratitis.”
Researchers say contact lens use is now the leading cause of bacterial keratitis in patients with healthy eyes in northern countries.
While vision loss from bacterial keratitis is uncommon, Acanthamoeba, although a rare cause, is one of the most serious.
It is responsible for about half of contact lens users who develop vision loss after keratitis.
About 90% of AK cases are associated with avoidable risks although the infection is still rare, affecting less than one in 20,000 annual contact lens wearers in the UK.
The most affected patients – a quarter of the total – end up with less than 25% of their vision or go blind after illness and face prolonged treatment.
The study indicates that 25% of sufferers generally require corneal transplants to treat the disease or restore vision.
The study, led by UCLA and Moorfields researchers, recruited more than 200 patients at Moorfields Eye Hospital who completed a survey, including 83 people with AK.
They were with 122 people who came to eye care clinics with other conditions.
The study found that people who wore reusable soft contact lenses (such as monthly lenses) had 3.8 times the odds of developing AK, compared to people who wore disposable contact lenses.
Showering with lenses increased the odds of AK by 3.3 times while wearing lenses overnight increased the odds by 3.9 times.
Among daily disposable lens wearers, lens reuse increased the risk of infection, while recent contact lens examination with a hygienist reduced risk.
“Previous studies have linked AK to wearing contact lenses in hot tubs, swimming pools, or lakes,” said first author, Associate Professor Nicole Karnett, University of New South Wales, Sydney, UCLA Institute of Ophthalmology and Moorfields Eye Hospital. We’ve added showers to this list, emphasizing that exposure to any water should be avoided when wearing lenses.
“Public swimming pools and coastal authorities can help reduce this risk by advising against swimming in contact lenses.”
Professor Dart added: “Contact lens packaging should include information on lens safety and risk avoidance, even if it’s as simple as ‘no water’ labels in every case, especially given that many people buy their lenses online without talking to a health professional.”
“Basic contact lens hygiene measures can go a long way in avoiding infection, such as washing and drying hands thoroughly before putting in lenses.”
The study, published in the journal Ophthalmology, was funded by Fight for Sight, NIHR Moorfields Biomedical Research Center, and Moorfields Eye Charity.